The present invention relates to the art of digital image defect correction. It finds particular application in conjunction with diagnostic imaging in fluorographic and fluoroscopic systems having flat panel radiation detectors and will be described with particular reference thereto. It is to be appreciated, however, that the invention will also find application in conjunction with CCD imagers, solid state image pickup devices, conventional x-ray diagnostic systems, computerized tomographic scanners, and other radiation detection systems for medical and non-medical examinations.
Typically, fluoroscopy includes a plurality of image intensifiers or two-dimensional, flat panel radiation detectors which convert X-ray radiation traversing a patient examination area into electronic signals. Each radiation detector includes a radiation sensitive face, such as a scintillation crystal, which converts the received radiation into a corresponding quantity of light. Solid state diodes are often provided to convert the light emitted by the scintillation crystal into analog electrical signals indicative of the intensity of the crystal emitted light, hence the intensity of the received radiation. The analog signals are converted into corresponding digital signals which are reconstructed into digital images.
Unfortunately, many flat panel radiation detectors, especially large-area flat panel detectors, contain single pixel defects, line defects, double-line defects, and column defects which lead to the generation of defective digital image representations. Prior art techniques correct such pixel, line, and column defects with a series of processes, typically consisting of defect map correction and median filtering. In defect map correction techniques, a base defect map of each panel detector is created during the manufacture of the flat panel detector. Additional defect maps may be created during subsequent calibrations of the panel detectors. These defect maps are used for the first order detection of permanent defects in the panels and interpolations, such as a median filter, are used to correct these permanent defects. A median filter algorithm is also applied to the entire image in order to provide secondary defect correction for random defects that do not have fixed patterns. This multi-phase defect correction process suffers from processing complexity and inefficiency.
Conventional median filter algorithms adjust all of the pixels of an image representation. In other words, each pixel of an image is replaced by the median value of the pixels in the neighborhood of the particular pixel being examined. This type of median filtering blurs images, which results in great reduction in image resolution. Further, conventional median filters cannot correct double line and double column defects. In fact, conventional median filters can introduce additional image defects by incorrectly replacing pixels adjacent to defective lines and columns with median values of neighborhood pixels.
The present invention contemplates a new and improved method for detecting and correcting digital image defects which overcomes the above-referenced problems and others.
In accordance with one aspect of the present invention, a method for real-time detection and correction of digital image defects due to defective detector pixels includes copying inputted image data which includes pixel values corresponding to each of a plurality of pixels of an image into a correction memory. For each pixel of the inputted image data, a kernel of nxc3x97n pixels is selected. The kernel contains a candidate pixel to be examined where the candidate pixel has an unprocessed pixel value. A median pixel value is calculated for the kernel. In addition, a threshold value based on the unprocessed pixel value of the candidate pixel and a predefined defect threshold is calculated. A difference value between the median pixel value and the unprocessed pixel value is calculated. The difference value is compared to the threshold value. In accordance with the comparing, either the candidate pixel value is replaced with the median pixel value or the candidate pixel value is retained.
In accordance with another aspect of the present invention, a method for detecting and correcting detector aberration defects in digital diagnostic images includes non-invasively examining a patient and generating diagnostic image data. The diagnostic image data is organized into a two or three-dimensional array of image pixel values. Each of a plurality of the pixel values is compared with a threshold criteria. In response to the compared pixel value passing the threshold criteria, the compared pixel value is retained. In response to the compared pixel value failing the threshold criteria, the pixel value is replaced with a value calculated from neighboring pixel values. The retained and replaced pixel values then form a corrected digital diagnostic image.
In accordance with another aspect of the present invention, a radiographic apparatus includes a penetrating radiation source which projects x-rays across an examination region. A plurality of radiation detector arrays are disposed across the x-ray examination region from the penetrating source. The detector arrays include analog-to-digital converters which convert analog signals into digital image signals. An image calibration processor performs image offset and gain calibration on the digital image signals. An adaptive median filter detects and corrects defects in the digital image signals due to defective detectors in the radiation detector arrays. The adaptive median filter includes a memory which stores each candidate pixel value and neighboring pixel values. A processor calculates a reference value from the neighboring pixel values. Further, the processor compares a relationship between the candidate pixel value and the reference value with a threshold criterion. Based on the comparison, the processor either replaces the candidate pixel value with a function of the neighboring pixel values or retains the candidate pixel value.
In accordance with another aspect of the present invention, a method of radiographic diagnostic examination includes propagating x-rays through a subject. With a two-dimensional radiation detector panel, the x-rays which have propagated through the subject are detected. The detected x-rays are converted into light signals and the light signals are converted into electrical signals. The electrical signals are then read out into an image representation. The image representation is scanned over on a pixel-by-pixel basis using an nxc3x97n kernel. A median value of each kernel is calculated for each scanned pixel. A deviation between the median value and a pixel value of the scanned pixel is calculated. The deviation is compared to a defect threshold. Based on the comparison, either the pixel value of the scanned pixel is replaced with the median value or the pixel of the scanned pixel is retained. At least a portion of the corrected image representation is then converted into a human-readable display.
In accordance with another aspect of the present invention, an adaptive filter for detecting and correcting digital image defects includes a memory which stores each candidate pixel value and each kernel containing each candidate pixel value and a plurality of neighboring pixel values. A processor reorders each kernel in order to calculate a median value for the kernel. The processor calculates a difference between the candidate pixel value and the median value. The processor then compares the difference to a defect threshold and based on the comparison, the processor either replaces the candidate pixel value with the median value or retains the candidate pixel value.
One advantage of the present invention is that it simplifies the detection and correction of defects in images acquired using flat panel radiation detectors.
Another advantage of the present invention is that it corrects image data dynamically on the fly without a priori mapping or calibration.
Another advantage of the present invention is that it corrects image defects without reducing overall image resolution.
Another advantage of the present invention is that it corrects double line and double column defects.
Another advantage of the present invention is that it corrects image defects without creating additional defects.
Yet another advantage of the present invention resides in its combining image defect detection and correction into a single procedure.
Still another advantage of the present invention is that it leaves most image data unaltered.
Other benefits and advantages of the present invention will become apparent to those skilled in the art upon a reading and understanding of the preferred embodiments.